LONG-TERM PERFORMANCE OF AN IN-SITU IRON WALL FOR REMEDIATION OF VOCS

The use of granular iron for in situ degradation of dissolved chlorina ted organic compounds is rapidly gaining acceptance as a cost-effectiv e technology for ground water remediation, This paper describes the fi rst field demonstration of the technology, and is of particular import ance since it provides the longest available record of performance (fi ve years), A mixture of 22% granular iron and 78% sand was installed a s a permeable ''wall'' across the path of a contaminant plume at Canad ian Forces Base, Borden, Ontario, The major contaminants were trichlor oethene (TCE, 268 mg/L) and tetrachloroethene (PCE, 58 mg/L). Approxim ately 90% of the TCE and 86% of the PCE were removed by reductive dech lorination within the wall, with no measurable decrease in performance over the five year duration of the test. Though about 1% of the influ ent TCE and PCE appeared as dichloroethene isomers as a consequence of the dechlorination of TCE and PCE, these also degraded within the iro n-sand mixture, Performance of the field installation was reasonably c onsistent with the results of laboratory column studies conducted to s imulate the field behavior, However, if a more reactive iron material, or a higher percentage of iron had been used, complete removal of the chlorinated compounds might have been achieved. Changes in water chem istry-indicated that calcium carbonate was precipitating within the re active material; however, the trace amount of precipitate detected in core samples collected four gears after installation of the wall sugge st that the observed performance should persist for at least another f ive years. The study provides strong evidence that in situ use of gran ular iron could provide a long-term, low-maintenance cost solution far many ground water contamination problems.